How to reduce amount of species in NEAT?
Your species count will increase as the chance of mutation increases. This is because in every generation, so many genes will be mutated that they have little resemblance of each other, and the distance function doesn't factor in historical markings / innovation numbers.

Try lowering the mutation rates.

Below is the distance function from here page 110

$$\delta = \frac{c_1E}{N} + \frac{c_2D}{N} + c_3 \cdot \overline{W}.  $$

If your fitness vary a lot, try ranking the fitnesses in each specie and setting the survival chance based on its rank.

If you mean a large action space by changing environment, you can set the number of output nodes to the total number of actions, and rank each action, best to worst, then pick the best available action for the state.